From 844c67369f72de6c89ad783b3fd1d59f8e8f4902 Mon Sep 17 00:00:00 2001 From: Michael Liang Date: Fri, 21 Aug 2026 12:15:27 -0600 Subject: fault-inject: fix dentry leak fault_create_debugfs_attr() has always taken an extra dentry reference on the created directory (attr->dname = dget(dir)) so that fail_dump() could print the name via %pd from any context. Nothing anywhere in the tree ever calls dput() on attr->dname. For callers with a matching teardown, that unmatched reference causes one dentry plus its attached inode to leak per fault_create_debugfs_attr / debugfs_remove_recursive cycle. simple_recursive_removal() drops debugfs's own +1 ref on the child dentry, but the dget()'d ref keeps its refcount at 1: the dentry ends up unhashed but pinned, and its inode is never freed. Boot-once callers (mm/failslab, block/blk-core, etc.) leak exactly once at init and never destroy the tree, so the impact there is bounded. But per-lifecycle callers (drivers/nvme, drivers/infiniband/hw/hfi1, drivers/mmc, drivers/iommu/iommufd, drivers/media, drivers/misc, drivers/gpu/drm/msm, drivers/crypto, net/sunrpc) leak on every create/destroy cycle. We observed this in production: an NVMe/RDMA host repeatedly reconnecting to a target that rejected the CRTO Property Get went through ~50 nvme controller create/destroy cycles per second, and dentry and inode_cache grew by ~13k pinned objects per 240 s -- unrecoverable through drop_caches. Byte math matched a per-cycle 1-dentry / 1-inode leak from the "fault_inject" directory dentry. Fix this by not holding any external reference in fault_attr. Embed the directory name as a fixed-size char array (FAULT_ATTR_DNAME_LEN, 64 bytes) inside struct fault_attr, copied by strscpy() at fault_create_debugfs_attr() time. fail_dump() prints it via %s. Advantages of an embedded array over kstrdup() + kfree() paired with a new destroy API: - Zero API footprint. No new export and no caller changes required: callers already own their fault_attr's memory and free it when they are done, and now that suffices. - No allocation on the create path. - fault_create_debugfs_attr() cannot fail from the name-copy step. - No lifetime coupling between attr->dname and debugfs; the string is valid for exactly as long as the containing struct. The 64-byte length accommodates every in-tree caller with generous headroom (the longest current name is "fail_dma_array_full", 19 chars). The user-visible fail_dump() format changes from "name %pd" to "name %s", but the printed content is identical -- %pd on the created directory renders the same string that was passed in as @name. drivers/infiniband/hw/hfi1/fault.c drops a now-invalid "attr.dname = NULL" statement; the surrounding kzalloc() already zero-initialises the array. Link: https://lore.kernel.org/20260821181527.3271414-1-mliang@purestorage.com Fixes: 6adc4a22f20b ("fault-inject: add ratelimit option") Signed-off-by: Michael Liang Signed-off-by: Andrew Morton Reviewed-by: Andrew Morton Cc: Akinbou Mita Cc: Dennis Dalessandro Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Vlastimil Babka Cc: --- include/linux/fault-inject.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h index 58fd14c82270..5c74748a53f3 100644 --- a/include/linux/fault-inject.h +++ b/include/linux/fault-inject.h @@ -18,6 +18,13 @@ enum fault_flags { #include #include +/* + * Length of the debugfs directory name embedded in struct fault_attr. + * Chosen to accommodate every in-tree caller of fault_create_debugfs_attr() + * (the longest is "fail_dma_array_full", 19 chars) with generous headroom. + */ +#define FAULT_ATTR_DNAME_LEN 64 + /* * For explanation of the elements of this struct, see * Documentation/fault-injection/fault-injection.rst @@ -37,7 +44,7 @@ struct fault_attr { unsigned long count; struct ratelimit_state ratelimit_state; - struct dentry *dname; + char dname[FAULT_ATTR_DNAME_LEN]; }; #define FAULT_ATTR_INITIALIZER { \ @@ -47,7 +54,6 @@ struct fault_attr { .stacktrace_depth = 32, \ .ratelimit_state = RATELIMIT_STATE_INIT_DISABLED, \ .verbose = 2, \ - .dname = NULL, \ } #define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER -- cgit v1.2.3